The invention relates to air filters and more particularly to electric air filters.
High efficiency particulate air (HEPA) filters are utilized in a number of different industries including the nuclear industry to prevent chemical contamination. In various applications, these filters should allow for recovery of collected dust and have less than 10 grams of residual deposit when the filter is discarded. The filter should operate at high temperatures and have high strength. The filters should have high efficiency at high flow rates. The filter designs should also be as compact as possible to lessen the impact on the overall system design.
The high efficiency of the HEPA filters results from the small size of the fibers utilized. However, adhesive used to bond the glass fibers together limits the temperature; HEPA filters are not operative at high temperatures over 300.degree. C. Even if the glass fibers were held together by sandwiching between high temperature resistance screens, the micro glass fibers have a relatively low melting point. For high temperature filtration, refractory fibers must be used. Unfortunately, they do not have sufficiently small fiber diameters for high efficiency air cleaning. However the efficiency of the filter mat made from high temperature resistance, non conducting fibers can be significantly increased by conversion to an electric air filter. An electric air filter removes particles from air electrostatically with a high efficiency and is consequently useful in many applications.
Through cost benefit analysis and field evaluations the most cost effective filtration system was determined to have a very high efficiency while providing the capability of being cleaned many times prior to its disposal. However, provided that the filter can be repeatedly cleaned the dust holding capacity does not have to be very high. Also, since high efficiency filter media have a high pressure drop the filter design must accomodate a large filtering surface. To accomodate a large filter surface within a relatively small volume the filter media must be packaged in a configuration that places the filtering surfaces in close proximity of each other. Unfortunately, packaging a large filter surface in a relatively small volume does not allow recovery of deposited material. As an example, the conventional HEPA filters utilize a pleated configuration of the filter media which makes the filtering surface inaccessible for filter cleaning since the pleats cannot be separated for cleaning.
Accordingly, it is an object of the invention to provide a high temperature electric air filter.
It is also an object of the invention to provide an electric air filter with high efficiency at high temperature over 300.degree. C.
It is a further object of the invention to provide a high temperature electric air filter having a maximum filtering surface which can be readily cleaned.
It is also an object of the invention to provide a high temperature electric air filter in which adjacent filter sheets can be separated during a cleaning cycle.
It is another object of the invention to provide a high efficiency electric air filter which can be cleaned many times prior to its disposal.